1. The Field of the Invention
This invention relates generally to the field of inks. In one particular aspect, the invention relates to writing and marking instruments containing liquid inks, and it more specifically relates to the formulation of permanent inks. In one preferred form, the invention relates to improvements in inks for marking instruments for permanent marking.
2. Brief Description of the Prior Art
There are disclosed in the prior art a number of both permanent and non-permanent inks. Inks generally are mixtures of a coloring matter dispersed or dissolved in a carrier fluid. The coloring matter, if readily dissolving in the carrier fluid, is termed a dye. An insoluble coloring material is termed a pigment. Pigments are finely ground solid materials and the nature and amount of pigment contained in an ink determines its color.
Writing and marker inks may also include such ingredients as humectants, biocides, and surfactants. Humectants function to improve freeze/thaw stability and to control drying out of the tip, while biocides serve the obvious function of preventing spoilage of the ink during the expected shelf life of the marker product. In order to limit graininess and/or to enhance the flow characteristics of the ink, a small amount of surfactant is ordinarily employed.
Water based writing and marker inks have traditionally been non-permanent. These prior inks are generally made by a mixture of water and a water soluble dye. While some water based marker inks may have the desirable quality of good skin and textile fugitivity, they also exhibit the undesirable quality of washing off of the writing surface. Water based writing and marker inks also tend to smear during application. After dispensed and dried, such inks are re-wettable and will again smear if later contacted with water. Water based writing and marker inks have also exhibited, at best, a very limited ability to adhere to nonporous surfaces.
Hydrocarbon solvent based writing and marker inks have traditionally been permanent inks. However, along with their desirable permanency, they have had several undesirable qualities. First, the solvent systems utilized in these inks typically include such toxic hydrocarbons as toluene and xylene. Such toxic components may lead to both disposal problems and consumer rejection due to a rising appreciation for the dangers of exposure to toxic chemicals.
Solvent based inks also have a very disagreeable odor due to their hydrocarbon components. Further, solvent based writing and marker inks traditionally are easily smeared and tend to "strike through" paper readily, soaking through the material to which they are applied instead of remaining on the surface. Moreover, solvent based permanent inks are usually difficult to wash from the skin.
A pigmented ink such as disclosed in U.S. Pat. No. 5,131,776 is a marked improvement over previously available inks and incorporates many of the beneficial features of previously available solvent based and water based inks. However, a familiar problem encountered with writing instruments using pigmented inks is that the pigment tends to settle during storage and shipping of the inks and markers using the inks. Pigmented aqueous based inks especially tend to demonstrate this settling while the marker is being stored. Such settling is believed to occur as a result of the low viscosity needed for a marker ink, approximately 1.0-4.5 c.p., and the difference in density between the pigment and the carrier medium, typically water.
Pigment settling may present a problem in a marker using a pigmented ink when the marker is stored either nib-up or nib-down. When a marker containing a pigmented ink is stored nib-down for an extended period of time, the pigment tends to settle into the nib on the writing tip. Such nib-down settling is usually recognized during later use of the marker as increased color intensity of the mark laid down by the marker. If such settling is sufficiently severe, blockage of the nib may occur.
When a marker containing a pigmented ink is stored nib-up for an extended period of time, the pigment tends to leave the nib and settle to the back end of the ink reservoir or transorb. Such settling can be recognized as a loss of color intensity in the mark laid down by the marker. In extreme cases of nib-up settling, the nib actually may appear to dry out.
Apparent from the foregoing is that an ink which has the combination of the desirable qualities of the typical water based, hydrocarbon solvent based, and pigmented inks would be very appealing to the consumer. An even more appealing writing and marker ink would retain these desirable qualities while eliminating the undesirable qualities of lack of toxicity, no "strike through", no disagreeable odors, no pigment settling and good skin fugitivity. In addition, the capability to adhere to nonporous surfaces such as glass, plastic or metals is, in certain applications, another desirable property. Such a writing and marker ink should also work with a variety of marking pen nib types including porous plastic, bonded fiber, composites, felt, extruded plastic and roller balls.
It is therefore a general object of the invention to provide an aqueous based permanent writing and marker ink in which pigment settling is avoided.
It is also an object of the invention to provide a nontoxic permanent writing and marker ink.
A further object of the invention is to provide a permanent writing and marker ink which exhibits little or no "strike through."
Another object of the invention is to provide a permanent writing and marker ink which adheres well to nonporous surfaces.
A still further object of the invention is to provide an odorless, or at least not malodorous, permanent writing and marker ink.
Yet another object of the invention is to provide a permanent writing and marker ink which can be dispensed through a variety of pen nib types.
It is a secondary objective of the invention to provide a permanent writing and marker ink with good skin fugitivity.
These and other objects and advantages of the invention will be apparent to those skilled in this art from the following description of the invention and the appended claims.